(Reuters Health) - Women taking the heart drug digoxin have an increased risk of breast cancer, according to a study of more than 2 million Danes. Digoxin, marketed as Lanoxin and Digitek, is used by people with heart failure or with abnormal heart beats. But it can also act like the female hormone estrogen in the body, leading researchers to wonder if it might up cancer risk the same way estrogen treatment does in older women.